So for what it's worth, should you need to convince your machine to talk with iOS 7.1, then here you get the latest 'libimobiledevice' and its dependencies 'libusbmuxd' and 'libplist' (because of this). And don't forget to follow the steps here, especially the part with gvfs, because that's how libgpod expects your iPhone to be mounted, even if you can access it through nautilus already.

And if you have a reason to use the latest gtkpod (v 2.1.4), just grab the compiled Debian package from the link mentioned above.
The trick to get gtkpod compiled for GTK 3.4 is to do the opposite of what's being suggested here (on Wheezy we need to get a reference from the old 'win->layout_manager->master' instead of the new 'gdl_dock_layout_get_master (win->layout_manager)' ) and to configure it without the '-Werror' flags (so warnings won't be treated as errors).

Now I could trick the iPhone to play a different file just by renaming it with the name of an existing file that had been purchased before. So it's just a matter of adding the correct references to the several database- and playlist files. I'll leave this up to the gurus of libgpod though.